Method and apparatus for forming a guide rib on a section of plastic film

ABSTRACT

A method and apparatus for forming a rib on a section of plastic film utilizes a roll having a groove, extrudes molten polymer into the groove, and places the section of plastic film in contact with the molten polymer in the groove. The molten polymer in the groove is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.

TECHNICAL FIELD

[0001] The present invention relates to thermoplastic storage bags, and more particularly to a method and apparatus for producing guide ribs for reclosable thermoplastic storage bags.

BACKGROUND ART

[0002] Thermoplastic storage bags having reclosable fasteners have been in wide use to store various items. One type of bag includes interengagable male and female closure elements or profiles that may be closed by pinching the elements together at one end thereof between a user's finger and thumb and sliding the user's opposed finger and thumb along the elements toward another end of the bag. One difficulty faced by a user of such a bag results from misalignment of the male and female closure elements of the bag as the user is attempting to seal the bag. Often, such misalignment prevents full closure of the bag and typically results in wasted effort and frustration by the user.

[0003] Attempts have been made over the years to provide a structure that facilitates closing of a bag by a user. An example of such a structure comprises a guide rib disposed on each side of the closure elements and extending parallel thereto. The guide rib(s) guide the user's finger and thumb as the user is attempting to close the bag so that the incidence of closure element misalignment is minimized.

[0004] Kamp U.S. Pat. No. 4,306,924 discloses an apparatus for producing a plastic container having occludable closure strips. The closure strips are supplied from a supply source and fed to a control roll, wherein the control roll in turn feeds the closure strips to an optional heating means that preheats a base portion of the closure strips. The closure strips are then transferred to a rotating casting cylinder having a pair of spaced apart circumferential grooves. The closure profiles are disposed in the grooves of the casting cylinder as the casting cylinder rotates and plastic film is extruded onto the casting cylinder to produce a plastic film with integral closure profiles.

[0005] Zieke et al. U.S. Pat. No. 4,741,789 discloses a method and apparatus for applying a profile and adjacent ribs to a traveling film web. The method comprises the steps of drawing a web of bag film over idler rolls into a forming and joining station. The forming and joining station includes a hopper for receiving plastic material, a body with heating means for heating and melting the plastic material and a screw auger for advancing the molten plastic material to a die block. The method further comprises the steps of applying a base member to the film by means of a polytetrafluorethylene-coated lay-on roller and extruding a male profile member, a first rib member and a second rib member as separate extrudates on a bag film web.

[0006] Geiger et al. U.S. Pat. No. 4,755,248 discloses a method and apparatus for producing a reclosable bag film. The method comprises the steps of drawing a film web from a die block around a driven rotatable casting roll and passing the film web over idler rolls to a closure member extrusion and joining station. A female profile is extruded from a first extruder and a male profile is extruded from a second extruder onto the film web as the film web passes around an idler roll at the station. The method further comprises the step of passing the film web and profiles around a chilled casting roll to cool the film web and profile.

SUMMARY OF THE INVENTION

[0007] According to one aspect of the present invention, a method of forming a rib on a section of plastic film includes the steps of providing a roll having a groove, extruding molten polymer into the groove, and placing the section of plastic film in contact with the molten polymer in the groove. The molten polymer in the groove is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.

[0008] In accordance with a further aspect of the present invention, a method of forming a pair of ribs on either side of a closure element carried by a section of plastic film includes the steps of providing a roll having a pair of grooves, extruding molten polymer into the grooves, and placing the section of plastic film in contact with the molten polymer in the grooves such that the closure element is disposed between the grooves. The molten polymer in the grooves is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the ribs.

[0009] In accordance with yet another aspect of the present invention, an apparatus for forming a rib on a section of plastic film includes a roll having a groove and an extrusion die for extruding molten polymer into the groove. A positioning system places the section of plastic film in contact with the molten polymer in the groove such that the molten polymer in the groove is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.

[0010] Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is an elevational view of a reclosable thermoplastic storage bag according to the present invention;

[0012]FIG. 2 is an enlarged, fragmentary, sectional view taken generally along the lines 2-2 of FIG. 1;

[0013] FIGS. 3-8 are sectional views similar to FIG. 2 illustrating alternative bags produced in accordance with the present invention;

[0014]FIG. 9 is an isometric view of a bag according to the present invention having intermittent ribs;

[0015]FIG. 10 is a fragmentary and enlarged elevational view of a portion of zipper tape according to the present invention;

[0016]FIG. 11 is an isometric view of an apparatus for producing bags according to the present invention;

[0017]FIG. 12 is a bottom elevational view of an extrusion die profile plate used in the apparatus of FIG. 11;

[0018]FIG. 13 is a cross-sectional view taken generally along the lines 13-13 of FIG. 11;

[0019] FIGS. 14-16 are isometric views similar to FIG. 11 of an alternate apparatus for producing bags according to the present invention;

[0020]FIG. 17 is a cross sectional view taken generally along the lines 17-17 of FIG. 16;

[0021]FIG. 18 is an isometric view similar to FIGS. 11 and 14-16 of an alternate apparatus for producing bags; and

[0022]FIG. 19 is an isometric view similar to FIGS. 11 and 14-16 of a still further alternate apparatus for producing bags.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Referring to FIG. 1, a reclosable pouch in the form of a thermoplastic storage bag 20 comprises first and second body portions 22, 24 joined to one another to form first and second bag walls 26, 28. The first and second bag walls 26, 28 are joined at first and second side portions 30, 32, respectively, and at a bottom portion 34. An opening 35 is disposed at a top portion 36 of the bag 20. A closure mechanism 38 and two lips 40 are also disposed at the top portion 36 of the bag 20.

[0024] Referring to FIG. 2, female and male closure elements 44 a, 44 b of the closure mechanism 38 are disposed on opposing inside surfaces 46, 48 of the first and second body portions 22, 24, respectively. According to a first embodiment, guide ribs 50 a, 50 b are disposed on the inside surface 46 of the first body portion 22 on either side of (i.e., flanking) the female closure element 44 a. The guide ribs 50 a, 50 b extend in a direction generally parallel to the closure elements 44 a, 44 b and are spaced sufficiently therefrom to guide a user's finger(s) and facilitate alignment of the closure elements 44 a and 44 b into interlocking engagement when sealing the closure mechanism 38.

[0025] The male closure element 44 b comprises a base 58 integral with flanking side members 54 and 56 and an arrow-shaped engagement member 60 that extends from the base 58. The female element 44 a comprises a base 62 with a C-shaped profile member 64 extending therefrom, wherein the female element 44 a is adapted to receive the male element 44 b when pressure is exerted on the closure elements by a user's finger(s) during closing of the bag. The side members 54 and 56 are of a sufficient size and proximity to the engagement member 60 such that the side members 54 and 56 move together with the member 60 when the members 60 and 64 are engaged and disengaged. The side members 54 and 56 also have a height which is less than the height of the engagement member 60, and the members 54 and 56 extend beyond tips 68 of the female profile member 64 when the engagement member 60 is engaged with the female profile member 64. Thus, at such time, the tips 68 of the female profile member 64 reside between the side members 54 and 56 and the male engagement member 60.

[0026] In a preferred embodiment, the guide ribs 50 a, 50 b are of the same height and such height is greater than the height of the female profile member 64. The guide ribs 50 a, 50 b can have any suitable cross-sectional configuration, such an inverted T-shape, as seen in FIGS. 2-4 and 7-8, an inverted Y-shape as seen in FIG. 6, a semi-circular cross-sectional shape as seen in FIG. 5, a triangular cross-sectional shape as seen in FIG. 5, etc . . . Preferably, the guide ribs 50 a, 50 b are spaced apart approximately 0.4 inches on center, are approximately 0.09 inches in height and have an approximate width of 0.067 inches at the widest point thereof.

[0027] If desired, a number of guide rib(s) 50 other than two may be provided. In the event that two or more guide ribs are provided, the guide ribs 50 may all have the same cross-sectional shapes and dimensions, or the cross-sectional shapes and/or dimensions may be different. The guide rib(s) 50 may be present in various different arrangements. Thus, for example, as seen in FIGS. 3 and 4, a single rib 50 c may be provided on either inside surface 46 or 48, wherein the rib 50 c is positioned and configured identically to either of the ribs 50 a, 50 b described above. In this case, the single rib 50 c can be disposed on a side of the member 60 or 64 toward the top portion 36 or toward the bottom portion 34 of the bag.

[0028] Other various configurations of guide ribs can be seen in FIGS. 5 and 6. In FIG. 5, two guide ribs 50 d and 50 e may be provided on the inside surface 46. The ribs 50 d and 50 e are positioned identically to the ribs 50 a, 50 b described above, but are configured such that the guide rib 50 d has a triangular cross-sectional configuration and the guide rib 50 e has a semi-circular cross-sectional configuration. The ribs 50 f and 50 g of FIG. 6 are configured identically to the ribs 50 a, 50 b described above, but are disposed on the inside surface 48.

[0029] Still more configurations of guide ribs are shown in FIGS. 7 and 8. FIG. 7 illustrates a first guide rib 50 h positioned on the inside surface 46 and a second guide rib 50 i positioned on the opposite inside surface 48, wherein the guide ribs are configured similarly to the ribs 50 a, 50 b as described above. In FIG. 8, a first set of guide ribs 50 j and 50 k is positioned on the inside surface 46 and a second set of guide ribs 50 m and 50 n is positioned on the inside surface 48. The ribs 50 j, 50 k are disposed within the ribs 50 m, 50 n and the ribs 50 j, 50 k, 50 m and 50 n are otherwise configured similarly to the ribs 50 a, 50 b as described above and shown in FIG. 2.

[0030] Preferably, although not necessarily, if two guide ribs 50 are positioned adjacent a closure element 44 a or 44 b, the guide ribs 50 may be spaced equidistant from and on opposite sides of the closure element. Also, if a single rib 50 is positioned on the inside surface 48 adjacent the male closure element 44 b and a second single rib 50 is positioned on the opposite inside surface 46 adjacent the female closure element 44 a, the guide ribs 50 are preferably (although not necessarily) disposed on opposite sides of the closure elements 44 a, 44 b and equidistant therefrom.

[0031] No matter what configuration is chosen, the guide rib(s) 50 provide raised portions that can be felt by a user's fingers when the user's fingers are brought into contact with one or both external surfaces 70, 72 of the bag walls 26, 28. The raised portion(s) act as a guide for a user's fingers to facilitate the engagement of the male and female closure elements 44 a and 44 b, and thus sealing of the bag 20.

[0032] If desired, one or more gripping ribs 74 may be disposed on the internal surfaces 46, 48 of the bag 20 between the closure elements 44 a and 44 b and the top portion 36 of the bag 20, wherein the gripping ribs 74 are integrally extruded with the walls of the bag. Any number of gripping ribs 74 can be used, although space is necessary between adjacent ribs in order to facilitate a gripping action with a user's fingers. In a preferred embodiment, about six or seven gripping ribs 74 are disposed on each lip 40 of the bag.

[0033] According to an alternate embodiment, one or more intermittent ribs may be provided, as opposed to the continuous ribs 50 a-50 n described above. FIG. 9 illustrates the second bag wall 28 of the bag 20, wherein two guide ribs 50 p and 50 q are disposed on the inner surface 48 parallel to and spaced apart from the male closure element 44 b and wherein the two ribs 50 p, 50 q extend intermittently from the first side portion 30 to the second side portion 32 of the bag 20.

[0034] Yet another embodiment as shown in FIG. 10 comprises a zipper tape 140. The zipper tape 140 includes first and second thermoplastic strips 142, 144, wherein female and male closure elements 44 a, 44 b are attached to or otherwise formed on the first and second thermoplastic strips 142, 144, respectively. Continuous or intermittent guide ribs 50 r, 50 s may be disposed on the first or second thermoplastic strips 142, 144, parallel to and spaced apart from the female or male closure elements 44 a, 44 b in any configuration as described above. Alternatively, a single guide rib or three or more guide ribs may be disposed on the strips 142, 144 as noted above. The zipper tape 140 may be attached to a folded thermoplastic sheet by any suitable conventional process and apparatus and the resulting structure may be severed and sealed at spaced locations to form individual bags.

[0035] Reclosable thermoplastic storage bags as described herein can be produced by any conventional bag-making process, such as a cast post applied process, a cast integral process, a blown process or any other process known in the art. Alternatively, any one of the processes implemented by the apparatus shown in FIGS. 11-19 could be used to produce the bag described herein.

[0036] If the female and male closure elements 44 a, 44 b are to be added to a section of film subsequent to the formation of one or more guide ribs 50 thereon, an apparatus as seen in FIGS. 11-13 can be employed. FIG. 11 depicts an apparatus for forming one or more ribs at high speeds that includes a rotatable first roll 160, a rotatable second roll 162, an extrusion profile die 166, and an air nozzle 168 disposed below the extrusion profile die 166. The extrusion profile die 166 includes a profile plate 167 having at least one, and preferably two outlet orifices 169, 171 through which molten polymeric material is extruded into a like number of associated grooves 173, 174, respectively, formed in the first roll 160 at a first axial end 160 a thereof. The grooves 173, 174 in the first roll 160 have the same cross-sectional shapes as the desired end shapes of the ribs 50. Preferably, although not necessarily, the grooves 173, 174 have cross-sectional shapes that are substantially identical to one another and the outlet orifices 169,171 have shapes that are substantially identical to one another. Also preferably, (although not necessarily, as noted below) each of the outlet orifices 169,171 has a shape similar or substantially identical to the cross-sectional shape of the associated groove 173, 174 of the first roll 160, whether that shape is an inverted T-shape, an inverted Y-shape, triangular, semi-circular, or another geometric shape. As seen in FIGS. 11, 15, 16 and 18, a positioning system 150 includes the second roll 162 and the film 172 and, in other embodiments such as FIG. 14, may include another rotatable roll 164.

[0037] In an alternative embodiment, the outlet orifices 169,171 have cross-sectional shapes that are substantially different than the cross-sectional shapes of the grooves 173, 174. For example, the outlet orifices 169,171 may have a circular shape while the grooves 173, 174 may be triangular in cross-section.

[0038] The method includes the steps of feeding molten polymer to extrusion profile die 166 by way of an extruder or melt pump and extruding molten polymer into the grooves 173, 174 of the rotating first roll 160 at an extrusion rate that ensures that the grooves 173, 174 are filled with molten polymer. Thereafter, the air nozzle 168 directs an air flow onto the molten polymer before it is deposited in the grooves 173, 174.

[0039] If desired, a different fluid may be directed against the molten polymer in the grooves 173, 174. Also, the single air nozzle 168 may be replaced by two air nozzles wherein each air nozzle directs air against molten polymer in an associated groove 173, 174. Still further, it is possible to eliminate the air nozzle 168 from this process; however, this may require greater positioning accuracy so that the extrudate falls exactly into the grooves 173, 174.

[0040] The method further includes the step of moving a section of plastic film 172 over the rotating second roll 162 toward the first roll 160 and into contact with the molten polymer in the grooves 173, 174. Thereafter, the section of plastic film 172 is drawn around a predetermined angular extent of the first roll 160, for example, one half to three quarters of the entire angular extent of the first roll 160. It is also preferred that the first roll 160 be chilled, preferably by passing water therethrough to facilitate bonding of the ribs to the film 172. As should be evident, the larger the diameter of the roll 160, the more cooling can be imparted to the ribs. If desired, water, air or another coolant can be directed against the outer surface of the film section 172 as the film 172 and ribs 50 are moving about the first roll 160 to aid further in cooling of the ribs.

[0041] Again, if the female and male closure elements 44 a, 44 b are added to the film in a step subsequent to the step of adding or forming guide ribs 50, another method implemented by the apparatus shown in FIG. 14 can be employed. The apparatus of FIG. 14 is similar to that of FIG. 11, except that it further includes a third rotatable roll 164 positioned below the second roll 162. During movement of the section of plastic film 172, the third roll 164 further presses the section of plastic film 172 overlying the grooves 173, 174 into intimate contact with the molten polymer in the grooves 173, 174 to facilitate bonding and proper formation of the ribs. The third roll 164 is controlled by a hydraulic actuator 175 that controls the amount of pressure exerted on the plastic film 172 by the third roll 164.

[0042] If the female and male closure elements 44 a, 44 b have already been applied to the film section 172, the embodiment of FIG. 15 can be employed to add or form the guide ribs 50. In FIG. 15, a rotatable roll 176 is situated adjacent the first roll 160. The method includes the same steps as described above in connection with FIGS. 11-13, except that pressure may be applied by the roll 176 against the roll 160 so that the film is brought into intimate contact with the molten polymer in the grooves 173, 174 without deforming the female and male closure elements 44 a, 44 b. Thereafter, the section of plastic film 172 is drawn around substantially the entire perimeter of the first roll 160. The position of the second roll 176 is controlled by hydraulic actuators 178 that control the amount of pressure exerted by the roll 176 on the roll 160.

[0043] If the female and male closure elements 44 a, 44 b have already been applied to the film section 172, the first roll 160 can include first and second additional grooves 182 a, 182 b, as seen in FIG. 16. The groove 182 a is disposed between the grooves 173, 174 at a first end 184 of the roll 160, while the second groove 182 b is disposed at a second end 186 of the roll 160. The grooves 182 a, 182 b accommodate the female and male closure elements 44 a, 44 b, respectively, in the event that the ribs are to be applied to the same side of the film section 172 as the closure elements 44 a, 44 b. FIG. 17 shows a cross-sectional view of the three grooves 173, 174 and 182 a of FIG. 16. The groove 182 a has dimensions that are just slightly larger than the cross-sectional dimensions of the female closure element 44 a so that the fit of the closure element 44 a in the groove 182 a is tight so that positioning accuracy is established and maintained. If desired, the male closure element 44 b may also have a tight fit within the groove 182 b to obtain further positioning accuracy.

[0044] As a still further alternative, where the ribs are to be applied to a side of the plastic film 172 opposite to the side that carries the female and male closure elements 44 a, 44 b, grooves may be provided in the first roll 160 and the second roll 162 (or the rolls 164 and/or 176, if used), as shown in FIG. 18. The groove 188 a is disposed at a first end 190 of the second roll 162, while the second groove 188 b is disposed at a second end 192 of the second roll 162. The grooves 188 a, 188 b accommodate the female and male closure elements 44 a, 44 b, respectively. The grooves 188 a, 188 b have dimensions similar to the grooves 182 a, 182 b of FIG. 16.

[0045] If desired, any or all of the rolls 162, 164 and 176 may be made of rubber or another deformable material that assists in applying pressure to the film while minimizing permanent deformation of the rib(s) and/or closure elements 44 a, 44 b.

[0046]FIG. 19 illustrates yet another alternative apparatus wherein a further pair of grooves 200, 202 substantially identical to the grooves 173, 174 are provided at a second axial end 160 b of the roll 160. An extrusion profile die 206 identical or similar to the extrusion profile die 166 is provided having outlet orifices aligned with the grooves 200, 202. The extrusion profile die 206 deposits extrudate into the grooves 200, 202 and the roll 162 presses the film 172 into intimate contact with the extrudate in the grooves 200, 202 to form ribs adjacent an edge 208 of the film 172 opposite an edge 210 at which the ribs 50 are formed in accordance with the apparatus of FIGS. 11-13. An air nozzle 212 directs air against the extrudate before deposit thereof into the grooves 200, 202. As in all of the preceding embodiments, once the ribs are formed by the apparatus of FIG. 19, the film 172 is folded lengthwise and severed and sealed at spaced locations to form individual bags, for example, as seen in FIG. 8.

[0047] If desired, the apparatus of FIG. 19 can be modified in accordance with the teachings of any of FIGS. 14-16 and 18.

[0048] As should be evident from the foregoing, the bag of FIG. 3 can be produced by any of the apparatus of FIGS. 11-17, so long as a single orifice is provided in the profile plate 167 and a single groove is provided in the roll 160. The same is true of the bag of FIG. 5, so long as grooves 173, 174 of different cross-sectional shape are provided in the roll 162. The bags of FIGS. 4 and 6 can be produced by the apparatus of FIG. 19, so long as the extrusion profile die 166 and the grooves 173, 174 are omitted and the desired number of orifices are provided for the die 206 and a like number of grooves are provided in the roll 160 at the second axial end 160 b. The bag illustrated in FIG. 7 can be produced by the apparatus of FIG. 19, modified as noted above to provide a single groove at each axial end 160 a, 160 b and a single outlet orifice for each die 166 and 206.

INDUSTRIAL APPLICABILITY

[0049] The bag described herein advantageously includes at least on guide surface that guides a user's fingers during closure of the bag. Thus, closing efficiency is increased and the expenditure of wasted effort by the user is minimized.

[0050] Further, the apparatus and method described herein extrude polymer from a profile die into grooves on a first grooved and cooled roller to create ribs. The still molten ribs are combined with a film and cooled as it rotates around the grooved roller. The use of grooves in the first roller to create the ribs allows the ribs to have a uniform size and shape, whereas, when molten polymer is extruded directly onto a film to create ribs, the ribs may deform or spread out.

[0051] The method described herein also has the advantage of being a continuous process that has relatively high production rates of up to or greater than 300 feet per minute. Other similar processes cannot reach such production levels because the time necessary to cool the ribs and film is longer.

[0052] Numerous modifications will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention and to teach the best mode of carrying out same. The exclusive rights to all modifications which come within the scope of the appended claims are reserved. 

I claim:
 1. A method of forming a rib on plastic film, the method comprising the steps of: providing a roll having a groove; extruding molten polymer into the groove; placing the plastic film in contact with the molten polymer in the groove; and allowing the molten polymer in the groove to cool below the melting point thereof while the plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.
 2. The method of claim 1, further comprising the step of providing a second roll for directing the plastic film toward the first-named roll.
 3. The method of claim 2, wherein the second roll is made of a deformable material.
 4. The method of claim 2, wherein the plastic film carries a closure element and wherein the second roll includes a groove that receives the closure element.
 5. The method of claim 2, further comprising the step of providing a third roll that presses the section of plastic film against the molten polymer.
 6. The method of claim 5, wherein the third roll is made of a deformable material.
 7. The method of claim 5, wherein the plastic film carries a closure element and wherein at least one of the first-named roll, the second roll and the third roll includes a groove that receives the closure element.
 8. The method of claim 1, wherein the plastic film carries a closure element and wherein the first-named roll includes a groove that receives the closure element when the plastic film is in contact with the polymer
 9. The method of claim 8, wherein the groove has dimensions larger than dimensions of the closure element.
 10. The method of claim 1, further comprising the step of providing an air knife that presses the plastic film against the rib.
 11. The method of claim 1, including the further step of chilling the roll.
 12. The method of claim 11, wherein the step of chilling comprises the step of passing water through the roll.
 13. The method of claim 1, further comprising the step of directing an air flow onto the molten polymer before the molten polymer is deposited into the groove.
 14. The method of claim 1, wherein the step of extruding comprises the step of operating an extrusion die having a profile plate wherein the profile plate includes an orifice having a shape similar to a cross-sectional shape of the groove.
 15. The method of claim 14, wherein the rib has an inverted T-shaped cross sectional shape.
 16. The method of claim 14, wherein the rib has a triangular cross sectional shape.
 17. The method of claim 14, wherein the rib has a semi-circular cross sectional shape.
 18. The method of claim 14, wherein the rib has an inverted Y-shaped cross sectional shape.
 19. The method of claim 14, further comprising the step of providing an air nozzle disposed below the extrusion die.
 20. A method of forming a pair of ribs on either side of a closure element carried by a section of plastic film, the method comprising the steps of: providing a roll having a pair of grooves; extruding molten polymer into the grooves; placing the section of plastic film in contact with the molten polymer in the grooves such that the closure element is disposed between the grooves; and allowing the molten polymer in the grooves to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the ribs.
 21. The method of claim 20, further comprising the step of providing a second roll for directing the plastic film toward the first-named roll.
 22. The method of claim 21, wherein the second roll is made of a deformable material.
 23. The method of claim 20, wherein the section of plastic film has first and second sides and wherein the closure element is disposed on the first side, the ribs are formed on the second side and the further roll includes a groove that receives the closure element.
 24. The method of claim 21, further comprising the step of providing a third roll that presses the section of plastic film against the molten polymer.
 25. The method of claim 24, wherein the third roll is made of a deformable material.
 26. The method of claim 24, wherein the third roll exerts pressure against the first-named roll.
 27. The method of claim 20, wherein the closure element and the ribs are disposed on a same side of the plastic film and wherein the roll includes a groove that receives the closure element when the section of plastic film is in contact with the polymer
 28. The method of claim 27, wherein the groove has dimensions larger than dimensions of the closure element.
 29. The method of claim 20, further comprising the step of providing an air knife that presses the plastic film against the ribs.
 30. The method of claim 20, including the further step of chilling the roll.
 31. The method of claim 30, wherein the step of chilling comprises the step of passing water through the roll.
 32. The method of claim 20, further comprising the step of directing an air flow onto the molten polymer before the molten polymer is deposited into the grooves.
 33. The method of claim 20, wherein the step of extruding comprises the step of operating an extrusion die having a profile plate wherein the profile plate has two orifices wherein each orifice has a shape similar to cross-sectional shape of the grooves.
 34. The method of claim 33, wherein each rib has an inverted T-shape cross-sectional shape.
 35. The method of claim 33, wherein each rib has a triangular cross-sectional shape.
 36. The method of claim 33, wherein each rib has a semi-circular cross-sectional shape.
 37. The method of claim 33, wherein each rib has an inverted Y-shape cross-secitonal shape.
 38. The method of claim 33, further comprising the step of providing an air nozzle disposed below the extrusion die.
 39. An apparatus for forming a rib on a section of plastic film, comprising: a roll having a groove; an extrusion die for extruding molten polymer into the groove; and a positioning system that places the section of plastic film in contact with the molten polymer in the groove such that the molten polymer in the groove is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.
 40. The apparatus of claim 39, further comprising a second roll that directs the plastic film toward the first-named roll.
 41. The apparatus of claim 40, wherein the second roll is made of a deformable material.
 42. The apparatus of claim 40, wherein the section of plastic film carries a closure element and wherein the second roll includes a groove that receives the closure element.
 43. The apparatus of claim 40, wherein the positioning system includes a third roll that presses the section of plastic film against the molten polymer.
 44. The apparatus of claim 43, wherein the third roll is made of a deformable material.
 45. The apparatus of claim 43, wherein the section of plastic film carries a closure element and wherein at least one of the first-named, second and third rolls includes a groove that receives the closure element.
 46. The apparatus of claim 39, wherein the section of plastic film carries a closure element and wherein the roll includes a groove that receives the closure element when the section of plastic film is in contact with the polymer
 47. The apparatus of claim 46, wherein the groove has dimensions larger than dimensions of the closure element.
 48. The apparatus of claim 39, wherein the positioning system includes an air knife that presses the plastic film against the rib.
 49. The apparatus of claim 39, wherein the roll is chilled by water.
 50. The apparatus of claim 39, wherein the positioning system includes an air nozzle that directs an air flow onto the molten polymer before the molten polymer is deposited into the groove.
 51. The apparatus of claim 39, wherein the extrusion die includes a profile plate wherein the profile plate includes an orifice having a cross-sectional shape similar to a cross-sectional shape of the groove.
 52. The apparatus of claim 51, wherein the rib has an inverted T-shaped cross-sectional shape.
 53. The apparatus of claim 51, wherein the rib has a triangular cross-sectional shape.
 54. The apparatus of claim 51, wherein the rib has a semi-circular cross-sectional shape.
 55. The apparatus of claim 51, wherein the rib has an inverted Y-shaped cross-sectional shape.
 56. The apparatus of claim 51, further comprising an air nozzle disposed below the extrusion die.
 57. The apparatus of claim 51, wherein the roll includes a further groove that receives molten polymer wherein the positioning system places the section of plastic film in contact with the molten polymer in the further groove to form a further rib. 